Chemical mechanical polishing slurry, its preparation method and use for the same

ABSTRACT

A chemical mechanical polishing slurry for polishing a copper layer without excessively or destructively polishing a barrier layer beneath the copper layer is disclosed and includes an acid, a surfactant, and a silica sol having silica polishing particles that are surface modified with a surface charge modifier and that have potassium ions attached thereto. A method for preparing the chemical mechanical polishing slurry and a chemical mechanical polishing method using the chemical mechanical polishing slurry are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.11/892,720, filed on Aug. 27, 2007; which in turn claims priority ofTaiwanese Application No. 095139197, filed on Oct. 24, 2006.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a chemical mechanical polishing slurry, moreparticularly to a chemical mechanical polishing slurry for polishing acopper layer without excessively or destructively polishing a barrierlayer beneath the copper layer. The invention also relates to a methodfor preparing the chemical mechanical polishing slurry, and a chemicalmechanical polishing method using the chemical mechanical polishingslurry.

2. Description of the Related Art

Chemical mechanical planarization is an essential technology in asemiconductor manufacturing process, and may affect the result of thefollowing photolithography. The planarization requirement for a surfaceof a wafer is more stringent due to the fact that the diameter of thewafer is increased, the wire width of the manufacturing process isminiaturized, and the integrated density of the components is increased.A chemical mechanical polishing (hereinafter referred to as CMP) processis used for the planarization of the surface of the wafer. An advantageof the CMP process is that it can solve the problem in which the focusdepth is reduced due to the lithography miniaturization during thephotolithography process for fabricating wafers having highly densifiedintegrated circuits.

A copper chemical mechanical polishing (hereinafter referred to as CuCMP) process is a two-step polishing process for the planarization ofthe surface of the wafer. Copper on the surface of the wafer is removedin the first step so as to expose a barrier layer, which is primarilycomposed of tantalum nitride or tantalum. The barrier layer is thenremoved in the second step. Each of the two steps is performed using aspecific polishing slurry. The polishing slurry for the first stepshould meet the requirements that the surface of the wafer should be asplanar as possible (i.e., the dishing and erosion levels should be aslow as possible), and that the polishing slurry should not cause damageto the barrier layer while achieving a high rate of copper removal.

A typical slurry for the Cu CMP process is composed of an acid or basesolution, which includes an acid or base component, water, surfactant,etc., and solid polishing particles dispersed in the solution. The acidor base solution is used to react with the copper on the surface of thewafer to form a copper oxide passivated film, which can be abradedmechanically by the polishing particles.

The polishing particles may be silica, alumina, zirconia, cerium oxide,silicon carbide, titania, silicon nitride, or combinations thereof.

Taiwanese Patent No. 1235762 discloses a slurry for polishingcopper-based metal comprising a silica polishing material, an oxidant,amino acid, a triazole compound, and water, wherein the weight ratio ofthe amino acid to the triazole compound ranges from 5 to 8, and whereinthe triazole compound is selected from the group consisting of1,2,3-triazole, 1,2,4-triazole, and the derivatives thereof. The silicapolishing material is silica polishing particles commonly used in theart.

Colloidal silica particles commonly used as polishing particles are madeby a wet chemical method which includes the steps of preparing a dilutesolution of a water glass (e.g., sodium water glass and potassium waterglass which are primarily composed of sodium silicate and potassiumsilicate, respectively) solution; passing the water glass solutionthrough a cationic exchange resin to remove metallic ions such as Na⁺and K⁺ from the water glass solution to form an aqueous active silicicacid solution; adding a basic agent to the silicic acid solution foralkalization at appropriate temperature and pH value to conductpolycondensation of active silicic acid to form particles of colloidalsilica; and ultra-filtering the particles of colloidal silica to obtaina silica sol. In consideration of safety, operating convenience, andproduction costs, the alkalization is usually conducted using sodiumhydroxide or sodium water glass.

Since the colloidal silica particles bear negative charge on thesurfaces thereof, they cannot be used advantageously in an acidicpolishing slurry for the first step of the Cu CMP process to remove Cu.It is well known in the art to treat the colloidal silica particles witha surface charge modifier to cationically modify the surface of thecolloidal silica particles. The details of the treatment with thesurface charge modifier are described in “The Chemistry of Silica”, R.K. Iler, Wiley Interscience (1979), pp. 410-441. For example, in the wetchemical method for preparing the colloidal silica particles, the saltof a metal, such as aluminum, chromium, gallium, titanium or zirconium,(e.g., sodium aluminate, or aluminium hydroxychloride can be used as thesurface charge modifier. The metallic cationic ions from the surfacecharge modifier bonded onto the surfaces of the colloidal silicaparticles modify the surface charge of the colloidal silica particles sothat the colloidal silica particles can be used stably in an acidicpolishing slurry useable for the first step of the Cu CMP process toremove Cu. U.S. Pat. No. 5,368,833 discloses a silica sol comprisingsilica particles having a specific surface area within a range from 750to 1000 m²/g and surface-modified with aluminum to a degree of from 2 to25% substitution of silicon atoms. The sol has an S-value within therange from 8 to 45%. It is disclosed in the patent that the sols areparticularly suitable for use as additives in paper making, and that theprocess disclosed therein is suitable for the production of sols havinga comparatively broad particle size distribution.

The process for the production of silica sols disclosed in the aforesaidU.S. patent starts from an alkali water glass (preferably, sodium waterglass). A water glass solution prepared from the alkali water glass isacidified and then alkalized to form silica particles, which are furtherprocessed by a cationic exchange resin treatment and a surfacemodification of the surfaces of the silica particles to obtain thedesirable silica sols. In Column 3, Lines 9-11 of U.S. Pat. No.5,368,833, it is described that the alkalization can be carried out withconventional alkali such as sodium, potassium or ammonium hydroxide,that it is preferred that alkalization is carried out by addition ofwater glass, and that potassium and sodium water glass, particularlysodium water glass, with a specific mole ratio of SiO₂ to M₂O, is usedin the alkalization.

Since polishing particles used in a CMP slurry must have a relativelyhomogeneous particle distribution to achieve a superior polishingresult, the sols having a comparatively broad particle size distributionas disclosed in U.S. Pat. No. 5,368,833 are not suitable for a CMPprocess. Moreover, such patent suggests nothing relating to a polishingslurry suitable for a CMP process.

U.S. Pat. No. 6,362,108 discloses a composition for chemical mechanicalpolishing comprising an acid aqueous suspension of cationized colloidalsilica containing individualized colloidal silica particles and water asthe suspension medium. The composition is used for polishing a layer ofinsulating material based on a polymer with a low dielectric constant.However, copper removal is neither taught nor suggested in this patent.

U.S. Patent Application Publication No. 2003/0094593 A1 discloses asilica and a slurry composition for chemical mechanical planarization.The silica comprises an aggregate of primary particles having an averagediameter of at least 7 nanometers, and a hydroxyl content of at least 7hydroxyl groups per nanometer squared. The slurry composition comprisesthe silica, and is used for the chemical mechanical planarization of asubstrate such as micro-electronic substrate by removing copper,tantalum, and silicon dioxide from the substrate.

As recited in claim 17 of US Pat. Publ. No. 2003/0094593 publication,the removal of tantalum is at a rate which is equal to or greater thanthe removal rate of copper. Therefore, the slurry composition disclosedin this prior art is suitable for removing tantalum, rather than copper.That is, the slurry composition is suitable for the second step of a CuCMP process for the removal of a barrier layer, rather than the firststep of the Cu CMP process for the removal of copper.

Therefore, it is desirable to provide a chemical mechanical polishingslurry for the removal of copper which will not cause damage to abarrier layer beneath a copper layer while providing a high efficiencyfor copper removal.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a chemical mechanicalpolishing slurry, which can remove a copper layer on a wafer efficientlyand which does not cause substantial damage to a barrier layer beneaththe copper layer.

Another object of the present invention is to provide a chemicalmechanical polishing method which uses the chemical mechanical polishingslurry.

A further object of this invention is to provide a method for making thechemical mechanical polishing slurry.

In the first aspect of this invention, the chemical mechanical polishingslurry for polishing a copper layer without excessively or destructivelypolishing a barrier layer beneath the copper layer according to thisinvention includes an acid, a surfactant, and a silica sol having silicapolishing particles that are surface modified with a surface chargemodifier and that have potassium ions attached thereto.

In the second aspect of this invention, the chemical mechanicalpolishing method according to this invention includes the steps ofcontacting a wafer with a polishing pad; supplying a chemical mechanicalpolishing slurry including a silica sol that contains silica polishingparticles to the wafer and the polishing pad, the silica polishingparticles being surface modified with a surface charge modifier andhaving potassium ions attached to the silica polishing particles; andplanarizing at least a portion of a surface of the wafer with thechemical mechanical polishing slurry.

In the third aspect of this invention, the method for preparing achemical mechanical polishing slurry that can polish a copper layerwithout excessively or destructively polishing a barrier layer beneaththe copper layer includes the steps of: decationizing a solution of asilicate through a cation exchanger to form silicic acid in thesolution; and alkalizing the silicic acid with potassium hydroxide orpotassium water glass to form silica polishing particles that havepotassium ions attached thereto.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will becomeapparent in the following detailed description of the preferredembodiments with reference to the accompanying drawings, of which:

FIG. 1 is a schematic view illustrating a molecular structure of aconventional colloidal silica particle;

FIG. 2 is an optical microscope photograph of a surface of a wafer afterbeing polished using a conventional chemical mechanical polishingslurry; and

FIG. 3 is an optical microscope photograph of a surface of a wafer afterbeing polished using a chemical mechanical polishing slurry of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to the present invention, a silica sol is prepared byalkalizing silicic acid with potassium hydroxide or potassium waterglass. While potassium hydroxide or potassium water glass is known to beusable as a base for alkalization, like sodium hydroxide or sodium waterglass, in preparing a silica sol or colloidal silica, the prior artneither teaches nor suggests that potassium hydroxide or potassium waterglass, when used as an agent for the alkalization of silicic acid, canprovide a silica sol that is particularly suited for the removal ofcopper by chemical mechanical polishing. Conventionally, an aqueoussolution of sodium hydroxide or sodium silicate is used as a base forthe alkalization in consideration of safety, operating convenience, andproduction costs.

Surprisingly, the applicants have found that when the alkalization isconducted using potassium hydroxide or potassium water glass instead ofsodium hydroxide or sodium silicate to form a silica sol, and when achemical mechanical polishing slurry produced from the silica sol isused in a Cu CMP process, the slurry can remove a copper layer on awafer efficiently without excessively or destructively polishing abarrier layer, such as a TaN layer, beneath the copper layer.

Referring to FIG. 1, a molecular structure of a conventional colloidalsilica particle is illustrated. Without being bound by any theory, it isbelieved that the colloidal silica particles obtained by thealkalization using potassium hydroxide may have a structure similar tothat shown in FIG. 1, except that Na⁺ will be substituted by K⁺ and thatH⁺ of the —OH group will be substituted by K⁺ to form the —OK group. TheK⁺ of the —OK group will be subsequently dissociated out of theparticles so as to form the colloidal silica particles bearing —O⁻. Thatis, the colloidal silica particles formed by the alkalization usingpotassium hydroxide have potassium ions attached thereto and bearnegative charges (i.e., —O⁻).

As described above, the chemical mechanical polishing slurry of thepresent invention includes an acid, a surfactant, and a silica solhaving silica polishing particles that are surface modified with asurface charge modifier and that have potassium ions attached thereto.Preferably, the potassium ions in the silica polishing particles are inan amount greater than 100 ppm, preferably greater than 200 ppm, basedon a total weight of the silica polishing particles.

The method for preparing the chemical mechanical polishing slurryincludes the steps of: decationizing a solution of a silicate through acation exchanger to form silicic acid in the solution; alkalizing thesilicic acid with potassium hydroxide or potassium water glass to formsilica polishing particles that have potassium ions attached thereto;surface-modifying the silica polishing particles with a surface chargemodifier; decationizing the solution through a cation exchanger so as toremove mobile cation from the solution after surface-modifying, thusforming a silica sol; and adding an acid and an surfactant to the silicasol so as to obtain the chemical mechanical polishing slurry.

The surface charge modifier suitable for this invention is well known inthe art. Preferably, the surface charge modifier is a metal oxide whichhas a valence number greater than +3 and which is aluminum, chromium,gallium, titanium, zirconium, or combinations thereof. More preferably,the surface charge modifier is an aluminate. Most preferably, thesurface charge modifier is sodium aluminate or potassium aluminate.

The chemical mechanical polishing slurry of the present inventionprovides an acidic environment for the silica polishing particles. ThepH value of the chemical mechanical polishing slurry of the presentinvention ranges preferably from 2 to 5, more preferably from 3 to 4.The silica polishing particles after the surface modification with thesurface charge modifier can be maintained stably and suitably in theacidic environment.

The acid contained in the chemical mechanical polishing slurry of thepresent invention is used for corroding the copper layer of the wafer.Preferably, the acids suitable for the present invention are malonicacid, succinic acid, pentanedioic acid, hexanedioic acid, itaconic acid,trans-butenedioic acid, acrylic acid, 2-hydroxy-acetic acid, formicacid, acetic acid, hexanoic acid, lactic acid, malic acid, tartaricacid, gluconic acid, citric acid, hydrochloric acid, sulfuric acid,cis-butenedioic acid, trans-butenedioic acid, 2,2-dimethyl-succinicacid, 2-ethyl-2-methyl-succinic acid, 2,3-dimethyl-succinic acid,itaconic acid, 2-methyl-cis-butenedioic acid, 2-methyl-trans-butenedioicacid, 2-methyl-2-hydroxy-acetic acid, 2-ethyl-2-hydroxy-acetic acid,2,2-diethyl-2-hydroxy-acetic acid, 2-ethyl-2-methyl-2-hydroxy-aceticacid, 2-methyl-acrylic acid, 2-ethyl-acrylic acid, 3-methyl-acrylicacid, 2,3-dimethyl-acrylic acid, 1,2,3,4-butane tetracarboxylic acid, orcombinations thereof. Preferable acids are succinic acid, pentanedioicacid, hexanedioic acid, itaconic acid, trans-butenedioic acid, acrylicacid, 2-hydroxy-acetic acid, formic acid, 1,2,3,4-butane tetracarboxylicacid, or combinations thereof. The amount of the acid preferably rangesfrom 0.01 to 5 wt. %, more preferably ranging from 0.1 to 3 wt. %, basedon the total weight of the chemical mechanical polishing slurry.

The surfactant suitable for this invention is an anionic surfactant or anonionic surfactant. Preferably, the surfactant is an anionicsurfactant. Preferably, the surfactant is used in the chemicalmechanical polishing slurry in an amount ranging from 0.01 to 1 wt %based on the total weight of the chemical mechanical polishing slurry.

Furthermore, additives commonly used in the art can be added into thechemical mechanical polishing slurry of the present invention, ifnecessary. The additives suitable for the chemical mechanical polishingslurry of the present invention include a biocide, a corrosioninhibitor, an oxidant, a stabilizer, or the like. The additives can beused alone or in combination.

Suitable corrosion inhibitors are benzotriazole, tricyanic acid,1,2,3-triazole, 3-amino-1,2,4-triazole, 3-nitro-1,2,4-triazole,4-amino-3-hydrazino-1,2,4-triazoyl-5-thiol, benzotriazole-5-carboxylicacid, 3-amino-1,2,4-triazole-5-carboxylic acid, 1-hydro-benzotriazole,nitro-benzotriazole, or the like, or any combinations thereof.Preferably, the corrosion inhibitor is benzotriazole.

Suitable oxidants are hydrogen peroxide, ferric nitrate, potassiumiodate, peracctic acid, potassium permanganate, or the like, or anycombinations thereof. Preferably, the oxidant is hydrogen peroxide.

The amount of the additive added to the chemical mechanical polishingslurry of the present invention may be determined according to theconditions or results of polishing the wafer. For example, if the levelof dishing occurring at the edge of the wafer is high, it can be loweredby increasing the amount of the surfactant. Additionally, if thepolishing rate of the wafer is lower than 3000 Å/min, it can be raisedby increasing the amount of the acid component and/or the amount of thesilica polishing particles.

The present invention also provides a chemical mechanical polishingmethod, which includes the steps of: (a) contacting a wafer with apolishing pad; (b) supplying the chemical mechanical polishing slurry ofthe present invention to the wafer and the polishing pad; and (c)planarizing at least a portion of a surface of the wafer with thechemical mechanical polishing composition.

The following examples are provided to illustrate the preferredembodiments of the invention, and should not be construed as limitingthe scope of the invention.

The following examples and comparative examples were carried out at roomtemperature and at ambient pressure unless otherwise stated.

Examples 1-4 Preparation of Chemical Mechanical Polishing Slurry

300 ml of sodium water glass was mixed with 2700 ml of de-ionized waterto form an aqueous solution of sodium silicate, which was passed througha cationic exchange resin column, thereby forming silicic acid. 5 wt %aqueous KOH was added gradually at a temperature below 80° C.(preferably, 70-80° C.) until the pH value of the aqueous solution wasgreater than 10 so that the silicic acid was alkalized and underwentpolycondensation. The reaction product was cooled to 40° C., and wasadded with 300 ml of 10 wt % sodium aluminate aqueous solution. After 40minutes, the reaction product was passed through a cationic exchangeresin column to obtain a clear silica sol A.

The silica sol A includes a plurality of silica polishing particles thatwere surface modified with sodium aluminate and that have potassium ionsattached thereto. The particle size of the silica polishing particlesdetermined by Malvern HPPS particle size analyzer of TREKINTAL CO. wasabout 10-50 nm.

The silica sol A was mixed with hexanedioic acid, an anionic surfactant,benzotriazole, and hydrogen peroxide in the amounts shown in Table 1 toobtain chemical mechanical polishing slurries.

Comparative Examples 1-3 Preparation of Chemical Mechanical PolishingSlurry

A silica sol B was prepared in a manner substantially similar to thatfor the silica sol A except that the alkalization was conducted using 5wt % aqueous NaOH. The silica sol B includes a plurality of silicapolishing particles that were surface modified with sodium aluminate andthat have sodium ions attached thereto.

The silica sol B was mixed with hexanedioic acid, an anionic surfactant,benzotriazole, and hydrogen peroxide in the amounts shown in Table 1 toobtain chemical mechanical polishing slurries.

Tests I. Determination of the Potassium Content

The potassium content in the silica polishing particles was determinedby a microwave-assisted acid digestion method. 0.1 g of silica polishingparticles were mixed with 10 ml of concentrated hydrofluoric acid toform a mixture. The mixture was added into a microwave digestionequipment (manufactured by Perkin Elmer Co., Model No. 2000), and wasreacted to obtain a suspension. After the suspension was removed fromthe equipment, the potassium content of a portion of the suspension wasdetected using an inductive coupling plasma spectrometer (manufacturedby Agilent Co., Model No. 7500C).

II. Polishing Test 1. Testing Conditions

(1) Instruments/Devices: (a) Polishing machine: manufactured by AppliedMaterials, Inc., Model No. AMAT/Mirra; (b) Polishing Pad manufactured byRohm & Haas, Model No. CUP4410; (c) Blank Cu wafer: manufactured bySemiconductor Manufacturing International Corp., China, having athickness of 20,000 Å; (d) Blank TaN wafer: manufactured bySemiconductor Manufacturing International Corp., China, having athickness of 3,000 Å; (e) Cu Patterned wafer: a wafer plated with a Cupatterned layer on a barrier layer of TaN, manufactured by Sematech,U.S.A., wire width of 0.18 μm.

(2) Instrument Settings: membrane pressure: 1.0-1.5 psi; initialpressure: 1.5-2.0 psi; down force pressure: 1.2-1.5 psi; inner tube:vent; retaining ring pressure: 1.8 psi; platen speed: 70 rpm; carrierspeed: 74 rpm; temperature: 25° C.; slurry flow rate: 200 ml/min.

2. Testing Procedure

The blank Cu wafer, the blank TaN wafer, and the Cu patterned wafer werepolished by the polishing machine using the chemical mechanicalpolishing slurries of the examples and the comparative examples. Thewafers were polished initially at the initial pressure for 10 seconds,followed by polishing at the down force pressure. The wafers after thepolishing procedure were washed by a washing device (Evergreen Model 10×manufactured by Solid State Equipment Corp.), and were dried by nitrogenpurging before conducting the following evaluation.

3. Evaluation

(1) Polishing Rate: The blank Cu wafer and the blank TaN wafer beforeand after the polishing procedure were tested using a resistivitymeasurement system (manufactured by KLA-TENCOR, U.S.A., Model No.KLA-Tencor RS-75) to measure the removed thicknesses of the Cu layer ofthe blank Cu wafer and of the TaN layer of the blank TaN wafer. Thepolishing rate is defined as the thickness removed within 1 minute, andis expressed in terms of Å/min. In the first step of the Cu CMP process,the commercially acceptable range for the polishing rate of the Cu layeris preferably above 3,000 Å/min. In general, the polishing rate of theTaN layer should be as low as possible.

(2) Dishing Level: The dishing level of an edge area of a wafer surfaceis measured by a contact surface profiler (manufactured by KLA-TENCOR,Model No. KLA-Tencor P-11). In general, the smaller the value, thebetter will be the dishing level.

(3) Surface Observation of a Cu Patterned Wafer After Being Polished:The center, edge, and middle portions of the barrier layer of the Cupatterned wafer after being polished were observed by an opticalmicroscope (manufactured by Olympus, Model No. MX50A/T, 1500×). Examplesof microscope photography are shown in FIGS. 2 and 3. The blackdistinctive profile shown in FIG. 2 indicates that the barrier layer(such as the TaN layer) was polished away, thereby exposing dielectriclayer (such as silica layer). Oppositely, the absence of the blackprofile in FIG. 3 indicates that the barrier layer was not polishedaway.

4. Results

i. The Potassium Content: The potassium contents in the silica polishingparticles determined by the microwave-assisted acid digestion method are264 ppm for Examples 1 to 3, and 212.4 ppm for Example 4.

ii. Polishing Test: The results of the polishing tests using thechemical mechanical polishing slurries of Examples 1-4 and ComparativeExamples are shown in Table 1, in which the concentrations or ratios ofthe components are determined on a weight basis. The term “Solidcontent” in Table 1 means the content of silica particles in each of theslurries. As for the surface observation of the Cu patterned wafersafter being polished, the symbol “O” represents the absence of thecontrasting black at the profile of the patterned components in themicroscope photograph, that is to say, the TaN barrier layer was notoverly polished and was not damaged. The symbol “X” represents thepresence of the distinctive black at the profile in the microscopephotograph, that is to say, the TaN barrier layer had substantial damageand was polished excessively. The symbol “Δ” represents slight damage tothe TaN barrier layer.

TABLE I Ex. 1 Ex. 2 Ex. 3 Ex. 4 Comp. Ex. 1 Comp. Ex. 2 Comp. Ex. 3Silica Polishing Particles Surface modified with sodium Surface modifiedwith sodium aluminate and having potassium ions aluminate and havingpotassium ions pH 3.96 3.94 3.50 3.50 3.90 3.90 3.50 Acid Hexanedioic0.4 0.4 0.4 0.4 0.4 0.4 0.4 amount acid (%) Formic acid (%) 0 0 0.1 0.10 0 0.1 Itaconic acid (%) 0 0 0.2 0.2 0 0 0.2 1,2,3,4-butane 0 0 0.0250.025 0 0 0.025 tetracarboxylic acid (%) Anionic surfactant (ppm) 15001500 2000 2000 1500 1500 2000 Solid content (%) 1 2 3 3 1 2 3Benxotriazole (ppm) 600 600 600 600 600 600 600 Hydrogen peroxide (%) 33 3 3 3 3 3 Initial Pressure (psi) 2.0 2.0 2.0 2.0 2.0 2.0 2.0 DownForce Pressure (psi) 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Cu polishing rate 57466270 6840 6740 5641 6319 6806 (Å/100 μm) TaN polishing rate 6 9 25 16 1520 121 (Å/100 μm) Dishing level 874 1045 752 774 1387 2055 1541 (Å/100μm) surface Center ∘ Δ ∘ ∘ x x x observation Edge ∘ Δ ∘ ∘ x x x of theCu Middle ∘ Δ ∘ ∘ x x x patterned wafer after being polished

Comparison Between Example 1 and Comparative Example 1

As shown in Table 1, the Cu patterned wafer after being polished by thechemical mechanical polishing slurry of Example 1 had no damage to theTaN barrier layer at the center, middle, and edge portions thereof,which indicates that the TaN layer was not overly polished so that theSiO₂ layer beneath the TaN layer was not exposed, and that the chemicalmechanical polishing slurry of Example 1 is useful for the first step ofthe Cu CMP process for Cu removal. On the other hand, the Cu patternedwafer after being polished by the chemical mechanical polishing slurryof Comparative Example 1 shows substantial damage to the TaN barrierlayer at the center, middle; and edge portions thereof.

Additionally, while the Cu polishing rate of Example 1 is substantiallyequal to that of Comparative Example 1, the TaN polishing rate ofExample 1 is merely about 40% of that of Comparative Example 1. Thedishing level of Example 1 is only 63% of that of Comparative Example 1.This indicates that Example 1 is superior to Comparative Example 1.

Comparison Between Example 2 and Comparative Example 2

As shown in Table 1, in the Cu patterned wafer after being polished bythe chemical mechanical polishing slurry of Example 2, merely slightdamage appears in parts of the TaN barrier layer at the center, middle,and edge portions thereof. However, in the Cu patterned wafer afterbeing polished by the chemical mechanical polishing slurry ofComparative Example 2, substantial damages appear in the TaN barrierlayer at all of the center, middle, and edge portions thereof.Therefore, as compared to the chemical mechanical polishing slurry ofComparative Example 2, the chemical mechanical polishing slurry ofExample 2 can avoid excessive polishing of the TaN layer.

Additionally, while the Cu polishing rate of Example 2 is substantiallyequal to that of Comparative Example 2, the TaN polishing rate ofExample 2 is merely about 45% of that of Comparative Example 2.Moreover, the dishing level of Example 2 is only 51% of that ofComparative Example 2. This indicates that Example 2 is superior toComparative Example 2.

Comparison Between Example 3 and Comparative Example 3

As shown in Table 1, the Cu patterned wafer after being polished by thechemical mechanical polishing slurry of Example 3 had no damage to theTaN barrier layer at the center, middle, and edge portions thereof,which indicates that the chemical mechanical polishing slurry of Example3 is useful for the first step of the Cu CMP process for Cu removaloppositely, the Cu patterned wafer after being polished by the chemicalmechanical polishing slurry of Comparative Example 3 had substantialdamage to the TaN barrier layer at the center, middle, and edge portionsthereof.

Additionally, while the Cu polishing rate of Example 3 is substantiallyequal to that of Comparative Example 3, the TaN polishing rate ofExample 3 is merely about 21% of that of Comparative Example 3.Moreover, the dishing level of Example 1 is only 48.8% of that ofComparative Example 3.

In view of the aforesaid comparison results, the chemical mechanicalpolishing slurry of the present invention is advantageous for the firststep of the Cu CMP process to remove Cu.

While the present invention has been described in connection with whatare considered the most practical and preferred embodiments, it isunderstood that this invention is not limited to the disclosedembodiments but is intended to cover various arrangements includedwithin the spirit and scope of the broadest interpretation so as toencompass all such modifications and equivalent arrangements.

1. A chemical mechanical polishing method, comprising the steps of: (a)contacting a wafer with a polishing pad; (b) supplying a chemicalmechanical polishing slurry including a silica sol that contains silicapolishing particles to the wafer and the polishing pad, the silicapolishing particles being surface modified with a surface chargemodifier and having potassium ions attached to the silica polishingparticles; and (c) planarizing at least a portion of a surface of thewafer with the chemical mechanical polishing slurry.
 2. A method forpreparing a chemical mechanical polishing slurry that can polish acopper layer without excessively or destructively polishing a barrierlayer beneath the copper layer, comprising the steps of: (a)decationizing a solution of a silicate through a cation exchanger toform silicic acid in the solution; and (b) alkalizing the silicic acidwith potassium hydroxide or potassium water glass to form silicapolishing particles that have potassium ions attached thereto.
 3. Themethod of claim 2, further comprising the steps of: (a)surface-modifying the silica polishing particles with a surface chargemodifier; and (b) decationizing the solution through a cation exchangerso as to remove mobile cation from the solution after surface-modifying,thus forming a silica sol.
 4. The method of claim 2, wherein thesilicate is sodium silicate.
 5. The method of claim 2, wherein potassiumhydroxide is added to the solution for alkalizing the silicic acid. 6.The method of claim 3, further comprising a step of adding an acid and asurfactant to the silica sol.